Destructive lesions with sclerosis from tumor new bone formation or reactive sclerosis. Occur almost exclusively in children and young adults (less than 30 years old).

Parosteal osteosarcoma features?

Arises from periosteum. Grows outside one, often wrapping around diaphysis without breaking cortex. Occurs in older age group than central osteosarcomas. Not as aggressive central osteosarcomas. Posterior distal femur is common location.

May mimic an early parosteal osteosarcoma of the posterior femur near the knee.

Cortical desmoid tumor. Myositis ossificans.

Ewing sarcoma features?

Permeative (multiple small holes) lesion in long bone diaphysis. May have onion-skin, sun-burst, or amorphous periostitis.

Any lesion in patient under 30 years. May be polyostotic. May have soft-tissue mass. May have bony sequestrum.

Nonossifying fibroma features?

Fibrous cortical defect (if less than 2cm). Asymptomatic (no periostitis). Metaphyseal. Emanate from cortex. 75% have thin sclerotic border that is scalloped and slightly expansile. Less than 30 years of age. Heal with sclerosis.

Lateral collateral ligament (LCL) of the knee consists of three parts, posterior to anterior:

Biceps femoris tendon inserts onto head of fibula. Fibular collateral ligament (true lateral collateral ligament) extends from lateral femoral condyle and joint biceps femoris tendon to insert on head of fibula. Iliotibial band extends from fascia to blend into lateral retinaculum on the patella and inserts at Gerdy's tubercle of lateral tibia.

Patellar Plica

"Rarely medial patella plica may thicken and cause symptoms similar to a torn meniscus. Can be removed arthroscopically quite easily.